No need to set this twice; StopSeeking sets it.

Author: SuuperW

src/BizHawk.Client.EmuHawk/MainForm.cs

@@ -3177,7 +3177,10 @@ private void StepRunLoop_Core(bool force = false)
 					{
 						Tools.TAStudio.StopSeeking();
 					}
-					PauseOnFrame = null;
+					else
+					{
+						PauseOnFrame = null;
+					}
 				}
 			}
 

src/BizHawk.Client.EmuHawk/tools/TAStudio/TAStudio.IControlMainForm.cs

@@ -103,7 +103,6 @@ public bool Rewind()
 				if (Emulator.Frame >= MainForm.PauseOnFrame)
 				{
 					MainForm.PauseEmulator();
-					MainForm.PauseOnFrame = null;
 					StopSeeking();
 					GoToPreviousFrame();
 				}

src/BizHawk.Client.EmuHawk/tools/TAStudio/TAStudio.ListView.cs

@@ -891,7 +891,6 @@ private void TasView_MouseWheel(object sender, MouseEventArgs e)
 					if (notch > 0 && Emulator.Frame >= MainForm.PauseOnFrame)
 					{
 						MainForm.PauseEmulator();
-						MainForm.PauseOnFrame = null;
 						StopSeeking();
 						GoToFrame(Emulator.Frame - notch);
 					}