Templar loosing execute bonus

DschiPeunt

I was experimenting with a magicka DPS build for my highelf templar the last days. Then I noticed that my DPS would sometimes get lower during the execute phases. I start executing at around 25% health. When checking my combat log it shows me that my execute ticks are around 4k, which roughly equals the damage it should do without any execute bonusses.
Did anyone else notice these problems? And does someone know if this happens only under special circumstances? Because I feel that it works sometimes and sometimes it doesn't.

I have already /bug-ed it but if others have the same problem, please report it too this makes any DPS-testing useless