Specifically, I noticed this when I moused over the display ammo next to the Kugelblitz I had in the hangar; all three ammo types are displaying the same amount of explosive filler. Yes, including the HVAP.
If HVAP and the explosive rounds show exactly the same filler value only in the hangar hover panel, this is likely a stat-card/UI mapping problem rather than proof that the shells use identical damage data in battle. The report should compare each shell’s full card and, if available, the protection-analysis result.
Please capture the Kugelblitz modification screen with every ammunition type selected, including shell names and filler values, and record the current client version/language. Then check whether switching language or reopening the client changes the display. A bug report should identify the expected value from an appropriate source and separate the UI inconsistency from any claimed damage-model issue. That keeps the report narrow and easily reproducible.