Shyness used to be and still considered as a virtue for females. It helps them save themselves from many dangers which they would have faced if they did not shy away and avoid the confrontation. Shyness is also considered in societies with ancient traditions and cultures behind them as an important female trait which is attractive and lovable.
Talking about the medical condition. I should agree with the contention that it is not a clinical condition to the extent that the medicinal system which do not look at a person as a complete whole, where a persons mind symptoms are not considered as a cause for ailments, there it is not a clinical condition. To my mind, all the symptoms the body is emiting should be considered together and should not be separated as clinical and psychtriac and the like. In fact, if a dominent mind symptom is present in a person and conventionally being referred to psychiatrist for opinion is not a right approach, rather a psychiatrist should be summoned and all doctors where the symptoms concerned are required should sit together and reach a unanimous conclusion. I know I am stretching a bit which is ideally not possible but then and then only a system of diagnosis is complete. Here I would call a general physician a complete physician than a specialist.
Coming back to the question. Only if the syness is evidently more than what is necessary, like ALWAYS hiding behind a pillar or cannot present a person himself before any strangers or any body coming to the house are the kind of symptoms which need medical attention, and may be included as a developmental problem which can end up in a behavioural problem.
In homeopathy, such cases are normally cured completely with future advantages, by the medicine Baryta Carb. In such cases, there is always a tendency in the subject to catch cold, tonsils swollen, perennial cough, adnoids swollen and the kind.
I do not think shyness is bipolar. Acute shyness or aggressively shy is something to be reckoned with. As far as the question is concerned, any body can be bipolar, shyness is not a pre-requisite.
I hope this helps.