It could be a Blizzard Bug or simply an oversight that they are allow customization of a frame that may need to be access during combat.
Seeing as taint reports may report one location as the problem when the problem was triggered elsewhere it is hard to know for definite where the problem is.
All you can do is report it as a but to them on the PTR and see if it is something they can identify/figure out/work around/fix etc.
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