Involuntary kegal is just automatic ejaculation reflex (like other reflexes in our body). In premature ejaculators, it occurs very early even from the start. Whereas in delayed ejaculators, it never occurs.
For me, it is a kind of indication that "point of not return" is just round the corner. The day I will eliminate these, I will be able to last at my will. During edging or ballooning, I don't feel these much. But during sex, these get out of control.

In another words, involuntary kegal happens when the sympathetic system tries to take over the control and prepares you for ejaculation. In premature ejaculators, parasympathetic system is weak and it tries to had over the control to sympathetic system.

(1) Parasympathetic Nervous System (PNS): It maintains the conscious or Voluntary Control = It controls earlier arousal levels (up to 7) or "Plateue Phase". Those who have strong PNS can last as long as they want. Their PNS is as strong as to keep things in its hands.

(2) Sympathetic Nervous System (SNS): Involuntary mechanism. It is responsible for ejaculation process. It activates when arousal level raises above level 7 and initiates the ejaculation process (which includes shutdown of the sphincter and contractions in the prostrate and the perineal muscles).

Involuntary kegals occur when your SNS tries to activate.

Every one feels involuntary kegals. Those who have strong PNS, do not feel it from the beginning or every now and then. They feel it only when they are ejaculating.

So how to make your parasympathetic system strong?
Exercise, yoga, lowering anxiety.