fitting MFI worktop upstands

A couple of years ago I fitted a MFI kitchen and used upstands on the worktops,these where fixed as flush as possible on to ceramic wall tiles and worktop with skirting adhesive and sealed with silcone sealant. However they have now started to bulge out as moisture seems to have got into to them(looks like they are made of mdf) Can any reader offer any other method of fixing and sealing or any other advice which will aid the lifespan of the upstands. TIA Gordon
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