When changing text on a slide, formatting is lost. See example code below:
	private boolean replaceTextInPowerPoint(final File destFile,
			final String assessmentId) {
		logger.log(Level.TRACE,
				"Entering WordDocGenerator.replaceVariablesInWordDoc(File, String)");
		boolean result = Boolean.FALSE;
		if (destFile.canWrite()) {
			FileInputStream is;
			final AnnexVarDao dao = new AnnexVarDao();
			final Map<String, String> variableRs = dao
					.loadVarReplacementMapByAssessmentId(assessmentId);
			final Map<String, String> summaryVars = dao
					.loadSummaryValuesByAssessment(assessmentId);
			final Map<String, String> qnAVars = dao
					.loadQuestionAndAnswerVarsByAssessment(assessmentId);
			if (summaryVars != null) {
				variableRs.putAll(summaryVars);
			}

			// 04/03/2012 [MJH] Change in regards to BUG: 72
			// Added Q&A section to the document.
			// For more detail, see Bugzilla at:
			// http://tlma.dimensiondata.com/bugs/show_bug.cgi?id=72
			if ((qnAVars != null) && (0 < qnAVars.size())) {
				variableRs.putAll(qnAVars);
			}
			final StrLookupDefaultReplace<String> strLookup = new StrLookupDefaultReplace<String>(
					variableRs);
			final StrSubstitutor subtitution = new StrSubstitutor(strLookup,
					StrSubstitutor.DEFAULT_PREFIX,
					StrSubstitutor.DEFAULT_SUFFIX,
					StrSubstitutor.DEFAULT_ESCAPE);
			try {
				if (0 < variableRs.size()) {
					is = new FileInputStream(destFile);
					final XMLSlideShow pptx = new XMLSlideShow(is);
					
					for(final XSLFSlide slide : pptx.getSlides()) {
						for (final XSLFTextShape textShape : slide
								.getPlaceholders()) {
							String shapeText = textShape.getText();
							logger.log(Level.DEBUG, String.format(
									"Got shape text%s%s",
									Configuration.SYSTEM_NEWLINE_STRING,
									shapeText));
							
							// 05/31/2012 [MJH] Change in regards to BUG: 89
							// Reducing the number of replacements that are done
							// where possible.
							// For more detail, see Bugzilla at:
							// http://tlma.dimensiondata.com/bugs/show_bug.cgi?id=89
							if (StringUtils.contains(shapeText, "${")) {
								shapeText = subtitution.replace(shapeText);
								textShape.clearText();
								logger.log(Level.DEBUG, String.format(
										"Replacing shape text on slide: %s",
										slide.getTitle()));
								textShape.setText(shapeText);
							}
							logger.log(Level.DEBUG, String.format(
									"New shape text%s%s",
									Configuration.SYSTEM_NEWLINE_STRING,
									shapeText));
						}
					}
					final FileOutputStream os = new FileOutputStream(destFile);
					pptx.write(os);
					result = Boolean.TRUE;
				}
			} catch (final FileNotFoundException e) {
				logger.log(Level.ERROR, e.getMessage(), e);
			} catch (final IOException e) {
				logger.log(Level.ERROR, e.getMessage(), e);
			}

		}
		logger.log(Level.TRACE,
				"Exiting WordDocGenerator.replaceVariablesInWordDoc(File, String)");
		return result;
	}