I too use IMAtch as my DAM software and also the reason I supported that PL focus more on developing tools such as photo stacking or improving their local adjustments sliders. When I realised my keywords were being corrupted in PL5 I raised the issue under
What does the Adobe announcement on LR mean for DXO and PL - #78 by akirstein
back in October where there were a reasonable amount of feedback. The disappointing fact is PL said they would get back to me but I am still waiting for a response. The best way to look after keywords in my opinion is IMatch as the developer knows his stuff and the platform is based on reconised structures. The best way to handle keywords in PL if you use another DAM software is turn off all syncing which unfortunately leads to double work as once you process the RAW file you then need to copy the keywords into the jpeg or tiff file. Really hope they either drop the effort (although I think this is too late and they may be wanting to compete with other developers such as Lightroom) or start getting it right like allowing us to use IMatch as a plugin.